Switching -hydrology distributed over to the superficially-hyperbolic way of updating pressure.  This makes Test P (test_29.py etc) errors slightly smaller except for bwp_avg which is slightly larger.  That is also the pattern with results from verifTestP.sh.  Because I am not certain I want to toss it out, I've hidden old code in new derived class.
Housekeeping: remove access of unused fields in the two versions of update().